"Electronics, Aug. 11, 1981, pages 97 to 103, describes a television receiver in which the subcircuit for demodulating the intermediate frequency is followed by two digital subcircuits for converting and processing the audio signal and the composite video signal. The demodulator has an audio-signal output which is coupled to the input of a first A/D converter, and a video-signal output at which only the composite video signal appears. The latter is fed to the input of a second, high-speed A/D converter which is suitable for the composite video signal, i.e., for sampling rates of about 18 MHz. Such high speed A/D converters are commercially available.
The signal appearing at the input of the television receiver is frequency-modulated with at least one audio signal, or in the presence of a stereo transmission, with two audio signals. The amplified input signal must be demodulated and filtered to obtain a first signal, containing only the audio signal, and a second signal, containing only the composite video signal. To this end, the prior art television receiver uses analog filters before the analog-to-digital conversion, so that division into an audio channel and a composite video channel takes place prior to the conversion.
The invention relates to such a circuit arrangement for filtering and demodulating a signal, frequency-modulated with at least one audio signal and contained in an input signal of a television receiver having a demodulator whose output is coupled to the input of an A/D converter suitable for converting a video signal from analog to digital form.
The prior arrangement has the disadvantage of requiring analog filters in the demodulator and two different A/D converters, which are relatively costly.